U. S. Nuclear Regulatory Commission Serial No. 09-003

VIRGINIA ELECTRIC AND POWER COMPANY
RICHMOND, VIRGINIA 23261
February 27,
U. S. Nuclear Regulatory Commission
Attention: Document Control Desk
One White Flint North
11555 Rockville Pike
Rockville, MD 20852
2009
Serial No.
NLOS/GDM
Docket Nos.
License Nos.
09-003
R1
50-338/339
NPF-4/7
VIRGINIA ELECTRIC AND POWER COMPANY
NORTH ANNA POWER STATION UNITS 1 AND 2
UPDATED SUPPLEMENTAL RESPONSE TO NRC GENERIC LETTER 2004-02
POTENTIAL IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY RECIRCULATION
DURING DESIGN BASIS ACCIDENTS AT PRESSURIZED-WATER REACTORS
By letter dated February 29, 2008 (ADAMS ML080650563), Virginia Electric and Power
Company (Dominion) submitted supplemental detailed information concerning
corrective actions taken in response to NRC Generic Letter (GL) 2004-02 for North
Anna Power Station (North Anna) Units 1 and 2. That letter fully detailed the corrective
actions that had been performed for GL 2004-02 at that time and specified the
corrective actions that were ongoing including: 1) downstream effects evaluations for
Emergency Core Cooling System (ECCS) and Recirculation Spray System (RSS) pump
seal performance and component wear, and 2) chemical effects testing and evaluation.
The required date for completion of the outstanding corrective actions for North Anna
Units 1 and 2 was extended from the original due date of December 31, 2007 to
November 30, 2008. [Reference NRC letter dated September 29, 2008 (ADAMS
ML082730022).]
Attachment 1 to this letter provides Dominion's updated supplemental response to GL
2004-02 for North Anna Units 1 and 2 and includes the necessary information to
appropriately address the analyses performed and corrective actions taken that were
not complete at the time of Dominion's previous supplemental response. These
corrective actions were completed for North Anna Units 1 and 2 by the November 30,
2008 due date. Final resolution of potential chemical and downstream effects on the
reactor core and flowpaths is pending the issuance of WCAP-16793-NP and the
associated NRC Safety Evaluation Report (SER). Corrective actions will be identified, if
required for resolution of this item, within 90 days of issuance of the NRC SER.
The content and level of detail provided in Attachment 1 are consistent with the
guidance included in NRC letter dated November 21, 2007 (ADAMS ML073110389)
and March 28, 2008 (ADAMS ML080230112) to the Nuclear Energy Institute.
vpi
Serial No. 09-003
Docket Nos. 50-338/339
Page 2 of 3
Attachment 2 provides responses to the remaining open items from the North Anna
Units 1 and 2 NRC GL 2004-02 Audit.
Should you have any questions or require additional information, please contact
Mr. Gary D. Miller at (804) 273-2771.
Sincerely,
ean Price
President - Nuclear Engineering
Commitment:
1. Corrective actions for resolution of potential chemical and downstream effects on the
reactor core and flowpaths will be determined and reported to the NRC within 90
days following the issuance of revised WCAP-16793-NP and the associated NRC
Safety Evaluation Report (SER).
Attachments:
1. Updated Supplemental Response to Generic Letter 2004-02, North Anna Power
Station Units 1 and 2
2. Response to Generic Letter 2004-02 Audit Open Items, North Anna Power
Station Units 1 and 2
COMMONWEALTH OF VIRGINIA
)
COUNTY OF HENRICO
)
)
The foregoing document was acknowledged before me, in and for the County and
Commonwealth aforesaid, today by Mr. J. Alan Price, who is Vice President - Nuclear
Engineering, of Virginia Electric and Power Company. He has affirmed before me that
he is duly authorized to execute and file the foregoing document in behalf of that
company, and that the statements in the document are true to the best of his knowledge
and belief.
Acknowledged before me this 2iI
My Commission Expires:
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Serial No. 09-003
Docket Nos. 50-338/339
Page 3 of 3
cc:
U.S. Nuclear Regulatory Commission
Region II
Sam Nunn Atlanta Federal Center
61 Forsyth Street, SW
Suite 23T85
Atlanta, Georgia 30303
NRC Senior Resident Inspector
North Anna Power Station
Mr. J. F. Stang, Jr.
NRC Project Manager
U. S. Nuclear Regulatory Commission
One White Flint North
Mail Stop 8G9A
11555 Rockville Pike
Rockville, Maryland 20852
Ms. D. N. Wright
NRC Project Manager
U. S. Nuclear Regulatory Commission
One White Flint North
Mail Stop 8H4A
11555 Rockville Pike
Rockville, Maryland 20852
Mr. J. E. Reasor, Jr.
Old Dominion Electric Cooperative
Innsbrook Corporate Center
4201 Dominion Blvd.
Suite 300
Glen Allen, Virginia 23060
Serial No. 09-003
Docket Nos. 50-338 and 50-339
ATTACHMENT I
UPDATED SUPPLEMENTAL RESPONSE TO GENERIC LETTER 2004-02
NORTH ANNA POWER STATION UNITS i AND 2
VIRGINIA ELECTRIC AND POWER COMPANY
(DOMINION)
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 1 of 42
UPDATED SUPPLEMENTAL RESPONSE TO GL 2004-02
NORTH ANNA POWER STATION UNITS I AND 2
1.0
Description of Approach for Overall Compliance
This information supplements the Overall Compliance information included in the
supplemental response to GL 2004-02 dated February29, 2008.
By letter dated February 29, 2008, Serial No. 08-0019, Dominion provided a
supplemental response to Generic Letter (GL) 2004-02, "Potential Impact of
Debris Blockage on Emergency Recirculation during Design Basis Accidents at
Pressurized-Water Reactors," for North Anna Power Station (North Anna) Units 1
and 2. This attachment updates the information that was previously provided.
The balance of this attachment provides the following items:
1.a
1.b
2.0
3.f
3.g
3.j
3.m
3.n
3.o
3.p
1.a
Conservatisms
Summary
General Description of and Schedule for Corrective Actions
Head Loss and Vortexing
Net Positive Suction Head (NPSH)
Screen Modification
Downstream Effects - Components and Systems
Downstream Effects - Fuel and Vessel
Chemical Effects
Licensing Basis
Conservatisms
Detailed analyses of debris generation and transport ensure that a bounding
quantity and a limiting mix of debris are assumed at the containment sump
strainer following a design basis accident (DBA). Using the results of the
analyses, conservative evaluations were performed to determine worst-case
strainer head loss and downstream effects. Chemical effects bench-top
tests conservatively assessed the solubilities and behaviors of precipitates
and applicability of industry data on the dissolution and precipitation tests of
station-specific conditions and materials. Reduced-scale testing was
performed by Atomic Energy of Canada Limited (AECL) using two separate
test facilities: Test Rig 33, a single-loop test rig and multi-loop Test Rig 89.
The reduced-scale testing established the influence of chemical products on
head loss across the strainer surfaces by simulating the plant-specific
chemical environment present in the water of the containment sump after a
Loss-of-Coolant-Accident (LOCA). These analyses included the
conservatisms discussed in the balance of this section.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 2 of 42
1. Test evaluations demonstrate that a fully formed thin-bed of debris takes
significant time (hours) to form and that formation of a thin-bed is
dependent upon disturbing settled debris throughout the test tank.
Consequently, a worst-case thin-bed of debris would be difficult to form
and would not be expected to form until several hours after sump
recirculation is initiated. Significant debris settling and sump water
subcooling occurs during the formation of a debris-bed so additional net
positive suction head (NPSH) margin is present for chemical effects
head loss. However, as a conservative measure, chemical effects testing
began with an established debris thin-bed on the strainer fin and was
conducted for the 30-day mission time.
2. The debris load in head loss testing was taken from the debris transport
calculation, which conservatively credits no particulate settling.
3. Debris introduction procedures in chemical effects testing ensured
minimum near-field settling and resulted in conservatively high debris
bed head losses.
4. Debris introduction was accomplished in a carefully controlled manner to
result in the highest possible head loss. Particulate was introduced
initially, which was followed by discrete fiber additions after the
particulate debris had fully circulated.
5. Only fines of fibrous debris were used in head loss testing as if all the
fibrous debris erosion, which is expected to take a considerable amount
of time, occurred at recirculation start.
6. Debris bed formation during testing included agitating (or "stirring") the
settled debris to ensure maximum debris on the strainer. However, any
turbulence in post-LOCA containment sump water is expected to be
localized to limited areas of the strainers. Consequently, much of the
sump water will be quiescent, which would promote debris settling.
7. Particulate settling in head loss testing was conservatively minimized
through use of a lower density walnut shell particulate as a surrogate for
the higher density epoxy coating particulate that may be present in postLOCA sump water.
8. Downstream wear analysis used the Large Break LOCA particulate load
to determine abrasive and erosive wear. This is a conservative
particulate loading, in view of the following:
•
Much of the particulate included in analysis is unqualified coating that
is outside the break zone of influence (ZOI). This unqualified coating
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 3 of 42
is assumed to dislodge due to exposure to the containment
environment. However, such dislodgement is likely only after many
hours, if at all.
The low velocity of the sump water column and the significant
number of surfaces throughout containment promote significant
settling of particulate in containment. Settled coating will not be
drawn through the sump strainer since the Recirculation Spray (RS)
strainer is located approximately six inches, and the Low Head
Safety Injection (LHSI) strainer is approximately 19 inches, above the
containment floor.
" The analysis assumes 100% strainer bypass of particulate
conservatively maximizing the effects of downstream wear.
9. Chemical effects testing results were conservative based upon several
conditions:
*
Aluminum corrosion amounts were calculated at high pH, where
aluminum corrosion and release rates are high. Testing was
performed at neutral pH, where aluminum solubility is low to
encourage aluminum compound precipitation. Sump water pH is
expected to be approximately 8 in the long-term.
*
The minimum sump water volume at specified times post-LOCA were
used to maximize the calculated sump aluminum concentrations.
" The analysis of aluminum load conservatively does not account for
the possible inhibitory effect of silicate or other species on aluminum
corrosion.
*
The rate of corrosion is maximized by analysis that does not assume
development of passive films, i.e., no aluminum oxides remain
adhered to aluminum surfaces. The formation of passive films could
be credited to decrease the corrosion and release rates at long
exposure times. Consequently, it is conservative to assume that all
aluminum released by corrosion enters the solution.
" All aluminum released into the solution is conservatively assumed to
transport to the debris-bed instead of plating out on the multiple
surfaces throughout containment. During bench-top testing,
aluminum plated out on glass beakers and, during reduced-scale
testing, aluminum plated out on fiber. It is reasonable to expect that
a portion of the aluminum ions released into solution will plate out on
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 4 of 42
some of the multiple surfaces in containment prior to arriving at the
debris-bed on the strainer.
Chemical effects test evaluations conservatively neglect the effect of
the presence of oxygen in the sump water. The corrosion rate of
aluminum in aerated pH 10 alkaline water can be a factor of two
lower than that measured in nitrogen-deaerated water. This data is
in NUREG/CR-6873, "Corrosion Rate Measurements and Chemical
Speciation of Corrosion Products Using Thermodynamic Modeling of
Debris Components to Support GSI-191."
10. NPSH margins were determined with the following conservatisms:
No credit was taken for additional NPSH margin in the short-term due
to subcooling of the sump water combined with the several hours
required to form the limiting thin-bed of debris. Our analyses
conservatively assume transport to the strainer following the break
occurs much sooner.
0
There is conservatism in scaling from test temperatures to higher
specified sump temperatures. The debris bed will expand slightly
when head loss is lower, i.e., at the higher sump temperature, the
bed would be expected to be slightly more porous than at the lower
test temperature. The assumption of a purely linear relationship
between head loss and viscosity when scaling to higher temperatures
is, therefore, conservative.
0
The NPSH calculations were guided by the observation that the
minimum margin would likely occur for the combination of parameters
that would minimize the containment pressure and maximize the
sump water temperature (and, hence the vapor pressure of this fluid),
thereby conservatively minimizing the contribution of containment
accident pressure to the calculated NPSH margin.
1.b Summary
The corrective actions associated with GL 2004-02 to resolve NRC Generic
Safety Issue (GSI) 191, "Assessment of DebrisAccumulation on PWR
Sump Performance,"have been completed for North Anna Units 1 and 2.
Downstream effects analyses (components) have been completed
consistent with WCAP-1 6406-P, Rev. 1, "Evaluation of Downstream Sump
Debris Effects in Support of GSI [Generic Safety Issue]-1 91," to identify any
wear, blockage or vibration concerns with components and systems due to
debris-laden fluids. Significant conservatisms are inherent in these
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 5 of 42
analyses, which provide reasonable assurance that downstream component
clogging will not occur, and downstream component wear will not
significantly affect component or system performance. The results of these
analyses are detailed in Section 3.m below.
Downstream effects analyses for the fuel and vessel -were previously
performed consistent with the methodology of WCAP-16793-NP, Rev. 0,
"Evaluation of Long-Term Cooling Considering Particulate, Fibrous and
Chemical Debris in the Recirculating Fluid," May 2007. However, since that
time, in response to concerns raised by the Advisory Committee on Reactor
Safeguards regarding WCAP-16793-NP, Rev. 0, the Pressurized Water
Reactor Owners' Group (PWROG) is performing additional testing and
analyses to more realistically determine the potential downstream and
chemical effects on the reactor core and the vessel/components. Corrective
actions will be identified, if required for resolution of this item, and submitted
to the NRC within 90 days following the issuance of the revised WCAP16793-NP and the associated NRC Safety Evaluation Report (SER).
Chemical effects testing and analyses have been completed for the LHSI
and RS strainers. AECL has performed various hydraulic tests that
simulated the actual debris loading and chemical conditions specific to
North Anna Units 1 and 2 based on debris generation, debris transport, and
chemical effects evaluationsi. Fibrous and particulate debris and chemicals
were added to a test rig to simulate the plant-specific chemical environment
present in the water of the containment sump following a DBA. Each test
was operated for more than 30 days after the formation of the debris bed
and initial chemical addition at specified temperatures and flow rates to
assess chemical precipitate formation and head loss change. These tests
verified that adequate NPSH is available to support the operation of the
LHSI and RS pumps during the post-LOCA recirculation mode. The
description of the analysis methodology, as well as the analysis and testing
results, are provided in Section 3.o below.
The completion of the evaluation of downstream effects on systems and
components and chemical effects testing resulted in changes-to information
submitted in Dominion's previous supplemental response dated February
29, 2008. Therefore, updated information is provided in Sections 3.f, 3.g,
and 3.j below.
Based on the methodology, modifications, and conservatisms described
herein, as well as the detailed information provided in Dominion's previous
supplemental response dated February 29, 2008, there is reasonable
assurance that long-term core cooling will successfully remove decay heat
for at least 30 days following a DBA.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 6 of 42
2.0
Description of and Schedule for Corrective Actions
This information supplements the Descriptionof and Schedule for Corrective
Actions information included in the supplemental response to GL 2004-02 dated
February29, 2008.
By letter dated February 29, 2008, Dominion indicated that the following actions
were on-going, and that an update would be provided:
1. Chemical and downstream effects testing evaluation.
2. Chemical effects bench-top testing.
3. Chemical effects reduced-scale testing.
4. Downstream wear evaluation for components.
5. Downstream wear evaluation for fuel and vessel.
Previously approved extension requests for North Anna Units 1 and 2 permitted
the completion of these actions by November 30, 2008.
Component downstream effects analyses have been completed using the
methodology described in WCAP-16406-P, Rev. 1, and those analyses and
relevant results are discussed in Section 3.m below. Information previously
provided on downstream effects for components and systems in the
supplemental response letter dated February 29, 2008 remains valid.
In-vessel downstream effects have been evaluated using WCAP-16406-P,
Rev. 1, and WCAP-16793-NP, Rev. 0, with acceptable results as described in
Section 3.n below. The NRC SER for WCAP-1 6793-NP has not been issued and
may contain staff conditions and limitations to be addressed. Dominion will
review the results of the staff SER when issued to determine if additional
analyses and corrective actions are required. If necessary, Dominion will submit
its plan to address any changes to the analysis of the in-vessel downstream
effects issue within 90 days of issuance of the final NRC staff SER on
WCAP-16793.
Chemical effects testing and analyses have also been completed. The testing
and analyses were completed using a methodology and testing protocol
developed with AECL at their Chalk River facility and observed, in part, by the
NRC staff. The description of the analysis methodology, as well as the testing
and analysis results, is discussed in Section 3.o below. Information previously
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 7 of 42
provided on chemical effects in the supplemental response letter dated
February 29, 2008 remains valid.
3.0
Additional Information for Head Loss and Vortexing (3.f), Net Positive
Suction Head (NPSH) (3.g), Screen Modification (3.j), Downstream Effects
Components and Systems (3.m), Downstream Effects - Fuel and Vessel
(3.n), Chemical Effects (3.o), and Licensing Basis (3.p)
-
The Dominion supplemental response to GL 2004-02 dated February 29, 2008
indicated in the response to RAIs 2, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, and 31 from
NRC letter dated February 9, 2006 (ADAMS ML060370463) that additional
information related to these requests would be provided when the downstream
effects and chemical effects evaluations were complete. Sections 3.m and 3.o
below provide additional information relevant to these RAIs.
3.f
Head Loss and Vortexing
This information supplements the Head Loss and Vortexing information included
in the supplementalresponse to GL 2004-02 dated February29, 2008.
The Dominion GL 2004-02 supplemental response dated February 29, 2008
provided containment sump strainer head loss information based on testing
without chemical effects. Chemical effects testing has been completed (see
Section 3.o) and revised allowable head loss values were determined for input to
the final strainer hydraulic analyses. The hydraulic analyses are performed to
identify NPSH margins for pumps taking suction from the containment sump
(Section 3.g) and to evaluate the effect of any predicted sump fluid flashing or
dissolved air released from solution in the strainer or at the pump suctions.
Containment sump strainer head loss is evaluated for two distinct time periods short-term and long-term. The short-term is defined as the time period from
event initiation to the point at which stable containment pressure, sump
temperature, and sump water level are achieved, which occurs within 6 hours.
During this initial period of the accident response, chemical effects are not
required to be considered in the determination of strainer head loss since
chemical debris would not have begun to influence the debris bed head loss for
several hours or days. The long-term considers containment conditions from 6
hours to 30 days and conservatively includes the maximum effect of aluminum
precipitation in the debris bed for the entire period.
The RS strainer flowrate for the short-term is defined by the operation of all four
RS pumps. Post-LOCA containment conditions stabilize below atmospheric
pressure within 6 hours and emergency operating procedures direct operators to
stop two of the four RS pumps. Therefore, for the long-term period, the RS
strainer flowrate is defined by the limiting set of two RS pumps in operation.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 8 of 42
Containment sump conditions and required pump flowrates were considered for
each time period, and the limiting condition for strainer head loss requirements
was determined for use in this evaluation. Final design and testing criteria for the
containment sump strainers are provided in Table 3.f-1.
Table 3.f-1: Final Design and Testing Acceptance Criteria for Sump Strainers
Total Strainer
Allowable
Water Level
Head Loss (ft
Flow Rate
Temperature
(ft.) above
H20)
(gpm)
(OF)
floor
Recirculation Spray
RS Short Terma
5.0
12,620
180
1.8
RS Long Terma
8.0
7500
104
6.7
Low Head Safety Injection
LHSI RMT Initiation
1.0
4050
113
5.0
(No Debris)
LHSI Short Terma
(after 2 Sump
5.0Q
4050
113
5.0
Turnovers)
LHSI Long Terma
8.5
4050
104
6.7
a. Short Term is defined as the time period from event initiation to the point at which stable
containment pressure, sump temperature, and sump water level are achieved (less than 6
hours). Long Term considers containment conditions from 6 hours to 30 days and includes the
maximum effect of aluminum precipitation in the debris bed.
Strainer Flashing
The potential for sump liquid flashing into vapor in the strainer system was reevaluated. The methods of analysis were the same as described in the
Dominion GL 2004-02 supplemental response dated February 29, 2008.
The analysis revealed that the onset of flashing is predicted for the North Anna
Unit 2 RS strainer (the worst-case RS strainer) when the debris bed on the fins
reached a pressure loss of 1.56 ft H2 0 or about 50% of the allowable debris
pressure loss of 3.11 ft H 2 0 at the bulk water temperature used in the flashing
analysis. If the pressure loss of the debris bed increases above this level, then
flashing is predicted in the strainer internal piping.
The condition for which the possibility of flashing was evaluated is a worst-case
low margin scenario occurring approximately 5 - 10 minutes after the RS system
is put in service. At this time a debris bed is'only just beginning to form on the
strainer fins. Testing performed by AECL has shown that several hours to days
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 9 of 42
are required for the full debris bed to form and to reach the point where maximum
debris pressure loss occurs. At the time the transient low margin condition
occurs, the pressure loss due to debris will be well below 50% of the full debris
pressure loss, and flashing will not occur within the strainer system.
The flashing analysis for the LHSI strainer concluded that there is significant
margin to flashing considering the maximum allowable strainer head loss.
Therefore, there is no concern for flashing in the LHSI strainer.
Air Inqestion
The potential for air ingestion was re-evaluated considering the results of
chemical effects testing. (There is no change to the vortexing evaluation results
provided with the Dominion GL 2004-02 supplemental response dated February
29, 2008.)'The analytical evaluation-for the allowable head loss limit shows a
small amount of voiding within the strainer system, and no voiding at the inlets to
the pumps, for the RS system. The LHSI strainer evaluation shows less than 1%
voiding in the strainer system, and a potential for up to 0.27% voiding at the
pump inlet for the short-term case and up to 0.47% voiding at the pump inlet for
the long-term case. Since there is no void formation at the RS pump inlet due to
air ingestion, no adjustment to required NPSH is necessary. Adjustment for
voiding was made for the LHSI pump in accordance with NRC Regulatory Guide
(RG) 1.82, Rev. 3, Appendix A methodology for void fraction less than 2%.
Consequently, the factor P3 1 + 0.5 * (void fraction) from RG 1.82 was'applied to
the required NPSH for the LHSI pumps (see Table 3.g-1). This small void
fraction would have insignificant impact on LHSI pump total developed head and
therefore, the delivered flowrate.
Hydraulic Analysis Results
The total allowable strainer head loss compared to the test results from chemical
effects head loss testing (described in Section 3.o) is provided in Table 3.f-2.
To encompass the effects of dissolved chemicals on the viscosity of sump water,
the calculations for strainer debris bed head-loss and internal head-loss include a
12% increase in water viscosity over that of clean water. This value is supported
by the chemical effects testing performed by AECL and the data from
NUREG/CR-6914, Vol. 1.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 10 of 42
Table 3.f-2: Hydraulic Analysis Results
Total Strainer
Strainer
Allowable
Internal
Head Loss, HUt Head Loss,
Debris Bed
Head Loss,
HLt > HLs + HLd
HLS (ft H20)
HLd (ft H 2 0)a
?
1.50
1.00
0.71
6.28
YES
YES
0.97
--
YES
0.93
1.72
YES
0.93
7.44
YES
(ft H20)
Recirculation Spray Strainer
RS Short Term
5.0
RS Long Term
8.0
Low Head Safety Injection Strainer
LHSI RMT Initiation.
1.0
(No Debris)
LHSI Short Term
(after 2 Sump
5.0
Turnovers)
LHSI Long Term
8.5
a.
These debris bed head loss results in ft H20 are equivalent to the debris bed head loss results
reported in Section 3.o in psi. The debris head loss includes the fin loss.
3.g
Net Positive Suction Head (NPSH)
This information supplements the Net Positive Suction Head (NPSH) information
included in the supplemental response to GL 2004-02 dated February29, 2008.
The Dominion GL 2004-02 supplemental response dated February 29, 2008
provided NPSH information based on containment sump strainer testing without
chemical effects. Chemical effects testing has been completed (see Section 3.o)
and hydraulic analyses have been performed incorporating the results of
chemical effects testing.
Revised NPSH margins were determined for the RS and LHSI pumps drawing
from the containment sump following a LOCA. NPSH margins were determined
at the time after a LOCA corresponding to lowest available NPSH for the shortterm and long-term cases. The NPSH margin was determined by subtracting the
total strainer allowable head loss and the required NPSH (NPSHr) from the
available NPSH (NPSHa), which was determined from the worst-case North Anna
GOTHIC containment analysis result and does not include the strainer head loss.
The total strainer allowable head loss establishes the design requirement for the
sump strainer. In most cases, containment analysis results provided an NPSHa'
value at a containment sump temperature that was greater than the head loss
test temperature. Conservatively, the allowable strainer head loss was specified
at test temperature without temperature correction, which provides an additional
unquantified margin in the head loss results.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 11 of 42
North Anna UFSAR Figures 6.2-66, 6.2-70, and 6.3-7 illustrate the trend of
available NPSH (without strainer losses) over time after an accident for the Inside
RS (IRS), Outside RS (ORS), and LHSI pumps, respectively.
As stated in Section 3.f, there is no void fraction at the RS pump inlets; therefore,
there is no adjustment required to the NPSHr for the RS pumps. A void fraction
of 0.27% short-term and 0.47% long-term is predicted at the LHSI pump inlets,
and the NPSHr was adjusted by the factor P3
from RG 1.82, Appendix A for less
than 2% void fraction.
NPSH margin calculation results based on maximum allowable strainer head loss
are provided in Table 3.g-1. Note that information in this table supersedes the
information in Table 3g-1 included in the February 29, 2008 supplemental
response.
The total allowable strainer head loss was compared to the test results from
chemical effects head loss testing (described in Section 3.o) in Table 3.f-2. All
sump strainer test results satisfactorily met the allowable head loss criteria. The
difference between the test results and the allowable head loss is not included in
the Minimum Margin values identified in Table 3.g-1 ,as an additional
conservatism.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 12 of 42
Table 3.g-1: Summary of RS and LHSI Pum Margins
Pump
Total Strainer
NPSHr (ft H20)
Allowable Head
at Maximum
Minimum Margin
Min. NPSHa (ft
Loss, HL (ft
H2 0)a
H20)b
Flowrate
(gpm)
(ft H20) = NPSHa
- HL - NPSHr
18.1 @ 193.2-F
5.0 @ 1800Fd
11.3 @ 3750
1.8
27.1 @ 104°F
8.0 @ 104°F
11.3 @ 3750
7.8
14.6 @ 204.3°F
5.0 @ 180°Fd
9.6 @ 3400
0.09
15.3 @ 198.4 0F
5.0 @ 180°Fd
9.6 @ 3400
0.7
28.0 @ 151.1°F
8.0 @ 104°Fd
9.6 @ 3400
10.4
14.7 @168 0 F
1.0 at 113oFd
13.4 @ 4050
0.3
22.4 @ 139.8°F
5.0 @ 113°Fd
15.21' @ 4050
2.19
26.6 @ 1040 F
8.5 @ 1040 F
16.55'@ 4050
1.55
ORSc -
Short
Terme
ORS Long
Terme
IRSc Short
Terme,f
IRS Short
Term ,h
IRS Long
Terme
LHSI RMT
LHSI -
Short
Terme
LHSI -
Long
Terme
a. This value is from the North Anna GOTHIC containment analysis and does not include strainer
head loss.
b. This value includes the debris bed and strainer internals head loss at the strainer flowrates
identified in Table 3.f-1.
c. ORS - Outside Recirculation Spray, IRS - Inside Recirculation Spray
d. Conservatively, no temperature correction has been made from NPSHa specified temperature.
e. Short Term is defined as the time period from event initiation to the point at which stable
containment pressure, sump temperature, and sump water level are achieved (less than 6
hours). Long Term considers containment conditions from 6 hours to 30 days and includes the
maximum effect of aluminum precipitation in the debris bed.
f. Two RS pumps in operation.
g. Although there is no margin available when compared to the specification for total strainer head
loss (5.0 ft H2 0), there is margin available to the test result of 2.21 ft H2 0 at 180OF - see Table
3Jf-2.
h. Four RS pumps in operation.
i. NPSHr is adjusted by P = 1 + 0.5 * (void fraction), i.e., NPSHr = 13.4 * 13.See Section 3.f for
discussion of void fractions predicted.
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Attachment 1
Page 13 of 42
3.j
Screen Modification
This information supplements the Screen Modification information included in the
supplemental response to GL 2004-02 dated February29, 2008.
Although the maximum opening size in the North Anna Units 1 and 2 sump
strainer fins is a 0.0625 inch diameter hole, the possibility exists for larger 'gaps'
in the strainer assembly due to fit-up inconsistencies. The potential for gaps up
to 0.125 inch wide for a total of 1% of strainer total flow area, and a limited
number of 0.1875 inch wide and 1 inch long gaps, was evaluated for its affect on
the downstream effects analysis described in Section 3.m.
Five areas of the downstream effects analysis that could be affected by
increased debris resulting from increased gap size were evaluated: (1) bypass
fraction and debris size, (2) downstream component wear, (3) downstream
component blockage, (4) fuels blockage, and (5) strainer hydraulics. The
evaluation concluded that the presence of 0.125 inch wide gaps for 1% of
strainer flow area, and 0.1875 inch wide by 1 inch long gaps limited to four on the
LHSI strainer and eight on the RS strainer, would have no significant effect on
the results of the downstream effects analyses for systems and components or
the fuel and vessel.
3.m
Downstream Effects - Components and Systems
This information supplements the Downstream Effects - Components and
Systems information included in the supplemental response to GL 2004-02 dated
February29, 2008.
The methodology used for downstream effects analysis was consistent with
WCAP-16406-P, Rev. 1, and the limitations and conditions described in the
accompanying NRC SER dated December 20, 2007 (ADAMS ML073520295).
No design or operational changes were required as a result of the downstream
effects evaluations.
This update of the downstream effects analysis addresses:
*
Wear of the High Head Safety Injection (HHSI) pumps (Charging pumps),
ORS pumps, IRS pumps, LHSI pumps, manually throttled valves, motor
operated valves, orifices, flow venturis, recirculation spray nozzles, and heat
exchangers, and an analysis of the wear effects on the performance of these
components,
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 14 of 42
*
Pressure relief which could potentially open and piston check valves which
will open during recirculation to determine if there is a possibility that the
valves will not reseat properly due to debris in the fluid potentially resulting in
an undesirable flow path for the recirculation fluid, and
*
Blockage of downstream components, including instrumentation, due to the
presence of debris.
Debris from the LOCA may pass through the containment sump LHSI and RS
strainers and enter the Emergency Core Cooling System (ECCS) and RS
System (RSS) causing abrasion and/or erosion on the surfaces of components.
Wear models were developed in accordance with the methodology provided in
WCAP-16406-P, Rev. 1, to assess the amount of wear in ECCS and RSS
components based on the initial debris concentration in the pumped fluid, the
debris concentration depletion due to settling and depletion, the hardness of the,
wear surfaces, and the mission time. The results for all downstream components
were determined to be acceptable per the criteria set forth in WCAP-16406-P,
Rev. 1.1
Wear Models
*
Abrasive Wear Models
Two abrasive wear models have been considered: the "free flow" type and
the "packing (or Archard's)" type. Free flow wear is the removal of material
due to hard or sharp particles that flow with the fluid between two closeproximity surfaces in relative motion to each other. In the Archard's model,
particles carried by the fluid adhere to the stationary surface by forming a
packing that wears the moving surface.
These types of wear affect, in particular, pump components such as wear
rings, impeller hubs, bushings, and diffuser rings. The wear rate of Archard's
model is constant and does not depend on the debris concentration and its
depletion over time. Once packing is established in the close running
clearances, debris depletion in the bulk fluid does not affect the rate of wear.
For the free flowing abrasive wear model, the rate of wear is a direct result of
the debris concentration in the fluid at any time during the pump (or other
component) duty cycle. Archard's wear is single sided since only the moving
surface is worn out, whereas the free flow model wears both the rotating and
the stationary surface individually and independently.
*
Erosive Model
Erosive wear is caused by particles impinging on a component surface or
edge and removing material from that surface due to momentum effects. This
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Docket Nos. 50-338 and 50-339
Attachment 1
Page 15 of 42
type of wear can occur in components with high velocity flows such as
throttling valves, orifices, heat exchanger tubes, and pump components.
The wear rate model includes the capability to calculate the initial debris
concentration, the debris concentration as a function of time, and the rate of
debris settlement. In addition to being captured by the sump strainer, debris
heavier than the recirculation fluid tends to settle out in the low velocity regions,
such as the reactor lower plenum. Therefore, the concentration of debris in the
recirculation flow will diminish with time.
The time-dependent concentrations of particulate and fibrous debris were used
as inputs to complete the evaluation of the effects of debris ingestion on ECCS
and RSS pumps, safety-related valves, heat exchangers, orifices, recirculation
spray nozzles, piping, and instrumentation tubing.
Pumps
The evaluation of pump hydraulic performance and mechanical dynamic
performance was based on design performance characteristics as a starting
point. This approach is supported by a review of approximately ten years of
inservice testing data that concludes that there has been no statistically
significant degradation of the performance of the HHSI, LHSI, IRS, and ORS
pumps over this time period.
Hydraulic Performance
Abrasive and erosive wear of pump internal subcomponents resulting from
pumping debris-laden water can cause an increase in the flow clearances of the
pump, which can result in increases in internal leakages and an overall decrease
in pump performance. ECCS and RSS pump wear was conservatively
calculated and the "worn" condition pump hydraulic performance was evaluated
for its effect on system minimum performance requirements. This overall system
performance evaluation also included a review of cumulative system resistance
changes due to wear in system piping and components to determine the impact
on system maximum flow to assess pump runout potential. The review of
component wear concluded that all system components pass the WCAP-1 6406P, Rev. 1, criteria. In addition, the system performance evaluation concluded
that there is no significant effect on system resistance or flowrates.
The overall system performance evaluation concluded that the ECCS and RSS
pumps meet their hydraulic performance requirements at the end of the 30 day
mission time.
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Docket Nos. 50-338 and 50-339
Attachment 1
Page 16 of 42
*
Mechanical Seal Wear/Performance
The impact of abrasive debris on the performance of pump mechanical shaft
seals has been evaluated for the LHSI, HHSI, and ORS pumps (IRS pumps do
not utilize a mechanical seal). The conclusion of the evaluation is that the debrisladen recirculation fluid would not adversely impact the performance of the
mechanical seals.
For the LHSI and ORS pumps with a tandem seal design, the inboard seal is
cooled by pump discharge water. The evaluation conservatively assumed that
the inboard seal failed due to wear from the debris-laden pumpage, and shaft
sealing was accomplished solely by the outboard seal. The evaluation
concluded that, since there is no significant convection of fluid to bring debris into
the outer seal and diffusion of debris is not credible due to the small clearances
between the stationary and pumping rings of the seal, the LHSI and ORS pumps
outboard seals would continue to function as required for the duration of the
mission time.
The HHSI pump shafts are sealed with single stage mechanical seals at each
end of the pump. The seals are cooled by pumped fluid. Following a LOCA, the
HHSI pumps initially take suction from the Refueling Water Storage Tank
(RWST) containing cooled, demineralized borated water such that the seal water
is initially clean at the start of the mission time. The potential for debris-laden
recirculation fluid to reach the seal cavity was evaluated to determine if seal
cooling could be degraded, seal faces could be worn excessively, or the seal
internal mechanism could be fouled preventing proper operation. The evaluation
concluded that the HHSI pump seals would be adequately cooled and seal faces
would not wear significantly from particulate debris during the mission time. In
addition, the amount of debris entering the seal chamber would be insignificant
such that the function of the seal internal mechanism would not be affected.
The seal analysis determined that no additional leakage is anticipated as a result
of debris-laden pumped fluid. Therefore, the HHSI pump seals meet
performance criteria and would continue to function as required for the duration
of the mission time.
*
Mechanical Dynamic Performance
The increased flow clearances resulting from the abrasive and erosive wear of
pump components were evaluated to determine if ECCS and RSS pumps would
operate satisfactorily, without excessive vibrations, to provide the required flow to
cool the core and depressurize the containment for the required mission time
post-LOCA.
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Docket Nos. 50-338 and 50-339
Attachment 1
Page 17 of 42
The LHSI, HHSI, IRS, and ORS pumps were found to satisfy the WCAP-1 6406P, Rev. 1, dynamic performance requirements criteria for the required 30 day
mission time.
However, the increased flow clearances due to wear calculated for the HHSI
pumps resulted in the potential for overpressurization of the pump outboard
mechanical seal. A detailed plant-specific analysis was performed by the pump
manufacturer to assess the wear of these pumps due to debris-laden pumped
fluid.
The pump vendor evaluation of HHSI pump internal wear was based on the
WCAP-16406-P, Rev. 1, methodology along with a detailed analysis of North
Anna-specific debris constituents. Specifically, since the testing referenced in
WCAP-16406-P, Rev. 1, that resulted in packing-type abrasive wear was
performed with coatings particulate debris, detailed debris characterization for
the North Anna debris-laden recirculation fluid were determined. The North Anna
debris mix consists of 70 ppm particulate, of which less than 10 ppm is coatings
debris. The pump vendor evaluation concluded that, since the WCAP-16406-P,
Rev. 1, tests resulted in packing formation observed at 920 ppm but not at 92
ppm coatings debris concentration, there is no concern for formation of packing
in the North Anna HHSI pump running clearances based on the low
concentration of particulate. Therefore, there would be no packing-type abrasive
wear over the HHSI pumps mission time.
Free-flow abrasive wear and erosive wear were determined to cause wear at
close clearance HHSI pump internals locations. The most critical diametral
clearance enlargement determined from the vendor analysis for a 30-day mission
time is 0.83 mils at the balance drum and is bounding for the other close
clearances within the pump. This calculated wear is within design tolerances for
the pump and will not affect pump mechanical dynamic performance or the
outboard mechanical seal pressure.
Heat Exchangers
Tube leakage or failure could occur due to excessive wall thinning as a result of
wear in heat exchangers. The heat exchangers in the recirculation flowpath have
been evaluated for wear effects dueto debris-laden fluid flow. The evaluation
concluded that the actual wall thickness of the heat exchangers tubes minus the
tube wall thickness lost due to erosion during a 30-day period is greater than~the
minimum wall thickness required to withstand both the internal tube design
pressure and the external shell design pressure. Therefore, the heat exchanger
tubes have sufficient wall thickness to withstand the erosive effect of the debrisladen water for a period of 30 days post-LOCA.
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Docket Nos. 50-338 and 50-339
Attachment 1
Page 18 of 42
In addition, tube blockage will not occur since the internal tube diameter is
greater than the maximum debris size and the flow velocity is greater than the
settling velocity.
Other Components
Manually throttled valves, motor operated valves, flow venturis, orifices, and RS
nozzles in the recirculation flow path were evaluated for the effects of wear due
,to the debris-laden fluid flow. These components were evaluated individually
and, with the exception of the plate orifices in the Safety Injection System
flowpath, were found to meet the criteria set forth in WCAP-16406-P, Rev. 1. A
system evaluation was also performed to determine the cumulative effect of wear
on system flowrates and the hydraulic performance requirements were
determined to be met. The wear of the plate orifices in the Safety Injection
System flowpath was included in the evaluation of system flow effects and found
to have an insignificant effect.
Relief valves in the recirculation flowpath have been evaluated for the ability to
reseat in the event of opening considering the debris-laden fluid. None of these
relief valves have the potential to lift during the recirculation phase; therefore, the
potential for debris blockage in the open position does not exist.
Piston check valves were evaluated for the potential to malfunction due to debris,
and it was determined that failure of the piston check valves to close would have
no effect on system functions required for the recirculation phase.
Instrumentation
Instrumentation, except for the Reactor Vessel Level Instrumentation System
(RVLIS), in the recirculation flow path that is required to function after a LOCA is
mounted either horizontally or vertically on top of the recirculation flowpath
piping, or the associated instrument sensing lines are oriented horizontally or
vertically (from above) at the pipe taps. The orientation of the instrument in the
pipe will allow the debris to continue flowing beyond the instrumentation.
The RVLIS measures reactor vessel water level with a differential pressure
transmitter connected through instrument tubing to the top and bottom of the
reactor vessel. There is no flow through the RVLIS tubing so debris would not be
drawn into the RVLIS connections. Additionally, no debris is expected to
accumulate in the reactor vessel upper head near the RVLIS connection. The
flows in the reactor vessel lower plenum during recirculation would be minimal,
so debris is expected to collect around the instrument nozzle penetrations, one of
which is used for the RVLIS connection. However, since the instrument nozzle
extends above the inside surface of the reactor vessel lower head, and there is
no flow through the RVLIS sensing tubing, debris would not collect near the
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 19 of 42
tubing open end in sufficient quantity to prevent the RVLIS from sensing lower
head pressure produced by vessel water level changes. The debris collecting in
the lower plenum would not affect RVLIS water level measurements.
Therefore, instrumentation will not be adversely affected by debris in the
recirculation flowpath.
3.n
Downstream Effects - Fuel and Vessel
This information supplements the Downstream Effects - Fuel and Vessel
informationincluded in the supplemental response to GL 2004-02 dated.
February29, 2008.
Dominion completed a LOCA Deposition Analysis Model (LOCADM) to quantify
the maximum expected deposition of chemical precipitates on the North Anna
Unit 1 and 2 fuel and the resultant maximum clad temperature. The results show
that the maximum clad temperature is approximately 375 0 F at the start of
recirculation. The maximum temperature is well below the acceptance criterion
limit of 800 0 F. The scale buildup starts at recirculation and reaches a maximum
of 967 microns (38 mils) at the end of 30 days. This value takes into account the
potential for strainer bypass and includes a factor of 2 times the expected
aluminum release and is well below the acceptance criterion of 1270 microns (50
mils). The results are essentially the same as shown in Figure 5-3 of WCAP16793-NP, Rev. 0. Thus, the conclusions of the WCAP for the fuel and vessel
analysis are applicable to North Anna Units 1 and 2 and demonstrate acceptable
long-term core cooling in the presence of core deposits.
Although this analysis to date has incorporated conditions and limitations
imposed on use of WCAP-16793-NP, Rev. 0, the initial NRC comments provided
for this technical report have been withdrawn and the WCAP is currently in
revision. The source of the revision is understood to be related to the fuel
blockage analysis, not the fuel deposit methodology. Upon issuance of revised
guidance, and the anticipated Regulatory Issue Summary to inform the industry
of the NRC staff's expectations and plans regarding resolution of this remaining
aspect of GSI-191, Dominion assumes that the existing analysis for North Anna
Units 1 and 2 will remain bounding of plant conditions and limitations on
LOCADM use in a final SER for WCAP-16793-NP. This assumption will be
confirmed through review of the revised WCAP-16793-NP and associated final
NRC SER. The results of this review will be reported within 90 days following
issuance of the final documents.
3.o
Chemical Effects
This information supplements the Chemical Effects information included in the
supplementalresponse to GL 2004-02 dated Febroary29, 2008.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 20 of 42
Overview
Dominion contracted AECL to perform chemical effects head loss testing and,
evaluation for North Anna Units 1 and 2. The methodology for chemical effects
testing and evaluation used observations of the Integrated Chemical Effects
Tests (ICET), the Westinghouse Owners Group document WCAP-16530-NP,
Rev. 0, "Evaluation of Post-Accident Chemical Effects in Containment Sump
Fluids to Support GSI-191," and various NRC-sponsored research presented at
public meetings or posted on the NRC website. Chemical effects bench-top tests
were performed and conservatively assessed the solubilities and behaviors of
precipitates, and the applicability of industry data on the dissolution and
precipitation tests to station-specific conditions and materials. Reduced-scale
testing was performed to establish the influence of chemical products on head
loss across the strainer surfaces by simulating the plant-specific chemical
environment present in the water of the containment sump after a LOCA.
Reduced-scale testing was conducted for greater than 30 days after the
formation of a debris bed and initial chemical addition at a specified temperature
and flow rate to assess the possibility of precipitate formation and any.
subsequent change in strainer head loss. These tests verified that adequate
NPSH is available to support the operation of the LHSI and RS pumps during the
post-LOCA recirculation mode.
Potential for Sufficient "Clean" Strainer Surface Area
North Anna Units 1 and 2 chemical effects head loss testing was conducted at
the AECL Chalk River Laboratories. It is expected that, due to debris settling and
very low pool velocities, much of the debris generated following a large break
LOCA will not reach the strainer. For a small break LOCA, even less debris
would be expected to reach the strainer. In addition, the strainer construction at
North Anna Units 1 and 2 spans a significant arc of the containment basement
annulus and debris from any particular break will likely be drawn to a localized
portion of the strainer rather than tend to cover the entire strainer surface.
Despite these factors that encourage the existence of open strainer surface area,
no credit is taken for open strainer surface area in the evaluation of head loss
due to chemical effects.
Debris-bed Formation
The worst-case strainer head loss is obtained for North Anna Units 1 and 2 with a
thin-bed of fibrous and particulate debris. Extensive testing without chemical
precipitants has determined that the thin-bed fiber thickness is nominally 1/4
inch. Since the fibrous and particulate debris constituent mixtures for North Anna
Units 1 and 2 are esse)ntially the same for any of the limiting break locations, the
break that produces the maximum particulate load produces the worst-case head
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Docket Nos. 50-338 and 50-339
Attachment 1
Page 21 of 42
loss when an approximately 1/4 inch thick fibrous bed is deliberately formed
following the addition of particulate. The same break that produces the worstcase head loss in the absence of chemical effects is expected to produce the
worst-case head loss with chemical precipitants added to the debris-bed. Debrisbed formation for the chemical effects testing followed the same procedure that
was used for previous head loss testing to ensure the worst-case debris-bed was
formed (i.e., head loss was highest). All of the particulate was added to the test
loop, which contained borated water with sodium hydroxide (NaOH) at pH 7 to
simulate the post-LOCA sump water. Once the particulate was well distributed
throughout the test loop water, fibrous debris was added. Fibrous debris was
prepared consistent with previous head loss tests to ensure individual fiber
separation and maximum head loss. Fibrous debris was added in four
increments, each of which had enough fiber to form a 1/16 inch thick fiber bed,
spaced to allow sufficient time for the debris to pack onto the strainer and begin
collecting particulate debris. No sodium aluminate additions to the debris bed
were made until after the head loss had stabilized.
Plant Specific Materials and Buffers
The sump pH buffer used at North Anna Units 1 and 2 is sodium hydroxide
solution that is sprayed in along with RWST water during quench spray pump
operation.
As described later under the AECL Method section, potential reactive materials in
containment have been evaluated and aluminum was determined to be the
chemical effects contributor of concern for the North Anna Units 1 and 2 sump
strainer evaluation. The total quantity of aluminum in containment has been
determined and categorized as either submerged, unsubmerged-sprayed,
unsubmerged-unsprayed, or encapsulated based on its exposure to sump or
spray water. Except for encapsulated aluminum, which does not contribute to
the aluminum in post-LOCA sump water, each category of aluminum was
evaluated for its contribution to aluminum in solution. Aluminum quantities for
North Anna Unit 2, which is the bounding unit, are as follows:
Exposure Category
Surface Area (ft2)
Mass (Ibm),
Submerged
185.5
1084.7
Unsubmerged - Sprayed
352.3
851.4
Unsubmerged - Unsprayed
392.7
1980.8
Containment sump water and spray temperature and pH have been evaluated at
various time periods following the LOCA. The worst case or bounding values of
pH and temperature were used in the analysis of aluminum corrosion (high pH,
4.
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Attachment 1
Page 22 of 42
high temperature) and precipitation (low pH). Containment sprays are assumed
to continue for the entire 30 days following a LOCA.
Approach to Determine Chemical Source Term
Chemical effects testing and evaluation were performed for North Anna Units 1
and 2 by AECL and consisted of a chemical effects assessment, bench-top
testing and reduced-scale tests.
Separate Effects
A plant-specific chemical effects assessment was performed using the AECL
method, which includes single-effects bench-top testing.
AECL Method
The AECL method for'assessment of chemical effects on strainer head loss was
audited by the NRC (Reference North Anna Power Station Audit Report dated
February 10, 2009, ADAMS ML090410626). The NRC staff visited Dominion's
Innsbrook facility from November 12-14, 2008, to perform a chemical effects
audit for North Anna Power Station Units 1 and 2. Prior to the on-site portion of
the audit, the staff reviewed relevant documents related to chemical effects
bench-top testing and integrated head loss test results for North Anna. The NRC
staff also visited AECL's Chalk River Facility on May 5-9, 2008, to observe
integrated chemical effects head loss testing for the Dominion plants. The NRC
staff reviewed the overall chemical effects approach, including the AECL test
facilities, North Anna safety systems drawing from the sump, observed
systematic non-chemical head loss differences, chemical effects head loss test
results, and analytical conservatisms. The audit report includes detailed
descriptions and evaluations of the head loss testing facilities. The report also
documents a detailed review of head loss testing results and a review of the
significant conservatisms incorporated into the sump strainer performance
analysis and an assessment of the post-LOCA NPSH margins. The NRC staff
concluded that the chemical effects audit of North Anna is complete with no open
items or requests for additional information.
The AECL methodology for the determination of chemical effects on sump
strainer performance consisted of three elements:
1. An assessment of potential precipitates, including determination of reactive
material amounts present in the containment sump pool, pH and temperature
profiles in containment, and a review of existing test and scientific literature
data.
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Docket Nos. 50-338 and 50-339
Attachment 1
Page 23 of 42
2. Bench-top testing to demonstrate that the solubility behavior of potential
precipitates determined from literature is reproducible under plant conditions
and to confirm that precipitates can be produced, if required, for reducedscale testing.
3. Reduced-scale testing to determine the influence of chemical products
present in the containment sump pool on the head loss across the ECCS
strainer.
Assessment of Potential Precipitates
AECL reviewed the published results of the Integrated Chemical Effects Tests
(ICET), the Westinghouse Owners Group document WCAP-16530-NP, and
various NRC sponsored research presented at public meetings or posted on
the NRC website. In addition, AECL representatives attended most of the
NRC public meetings on chemical effects in 2006 and 2007 and reviewed all
of the relevant presentations from these meetings. The following conclusions
were drawn from the data reviewed:
1. The ICET tests clearly show that, at the pH values studied, aluminum
corrosion can give rise to the formation of an aluminum-bearing
precipitate. However, the tests also show that:
a) Aluminum corrosion may be inhibited by species present in the sump
environment (e.g., phosphates, silicates).
b) The precipitate formed included boron. The presence of boron can
affect the mass or flocculation properties of the aluminum-bearing
precipitate formed.
'2. For the surface areas of materials used in these tests, only low
concentrations of iron, nickel, magnesium and zinc dissolved into the
simulated sump water, and these species did not lead to the formation of
significant amounts of precipitates.
3. Significant concentrations of silicon and calcium from dissolution of
fiberglass'and Cal-Sil can be present in the sump solutions. If trisodium
phosphate (TSP) is present, precipitates containing calcium and
phosphate, or calcium, phosphate and carbonate, can form. In the
absence of TSP, the calcium and silicon do not lead to the formation of
significant chemical precipitates.
4. Concrete does not appear to be a significant source of calcium in solution.
5. Thermodynamic modeling alone cannot properly predict the identity or
quantities of precipitates formed under PWR sump conditions; kinetic
factors are very important.
6. There is no evidence of direct chemical effects from paint debris.
7. While WCAP-16530-NP suggests that sodium aluminum silicate is a
possible precipitate, a review of the literature on the thermodynamics and
(-
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Attachment 1
Page 24 of 42
kinetics of aluminosilicate formation suggests that this is unlikely under
PWR post-LOCA sump water conditions.
Based on these conclusions, it was further concluded that in PWR post-LOCA
containment sump water, only two precipitates would be of concern:
aluminum hydroxide or oxyhydroxide, and calcium phosphate (likely
hydroxyapatite). Since North Anna Units 1 and 2 do not use TSP as a pH
buffer for the sump water, only the formation of aluminum hydroxide was
further evaluated. This evaluation was based on the available experimental
data including ICET tests, WCAP-16530-NP, and data from the reviewed
literature.
The AECL study used the basic methodology outlined in WCAP-1 6530-NP to
calculate the mass of aluminum released. However, rather than use the
WCAP-16530-NP release equation, the data from WCAP-16530-NP and
other sources were used by AECL to develop a semi-empirical release
equation. To model the aluminum release rate, the pH and temperature
dependencies of the corrosion rates were evaluated separately. This allowed
better comparison with existing literature data on aluminum corrosion. AECL
determined aluminum corrosion rate expressions based on pH and on
temperature from review of literature data. The time dependence of the
corrosion rate was also evaluated but no term for the time dependence was
included in the final release model. Neglecting time dependence was
considered to be a conservatism.
Containment aluminum inventories can be divided into exposure categories of
submerged, unsubmerged-sprayed, unsubmerged-unsprayed, or
encapsulated based on its exposure to sump or spray water. Except for
encapsulated aluminum, which does not contribute to the aluminum in postLOCA sump water, each category of aluminum was evaluated for its
contribution to aluminum in solution. Each category has a temperature
evolution profile and a worst-case scenario pH. In addition, unsprayed
aluminum has a limited time period during which transport of aluminum
corrosion products to the sump can occur, which limits its contribution to the
sump aluminum concentration.
The aluminum released to the containment sump was calculated based on
the aluminum surface areas and sump and spray water pH based on the
correlation:
ALUMINUM RELEASE OVER INTERVAL =
CORROSION RATExINTERVAL LENGTHxALUMINUM SURFACE AREA
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where CORROSION RATE (i.e., aluminum release rate) is dependent upon
pH and temperature and is determined from the following equation developed
by AECL:
Release Rate (mg/m 2 ,s) = 55.2 • exp (1.3947 • pH - 6301.1 • T-1),
where T is in degrees Kelvin. The results of the application of the AECL
release rate model was compared to the WCAP-16530-NP model results
using North Anna aluminum inventories and were found to predict a greater
30-day release of aluminum.
For unsubmerged-unsprayed aluminum, a detailed heat transfer and
condensation evaluation was performed to determine the time required to
equalize the temperature between the aluminum surface and the containment
environment. When the temperature is equalized, no further condensation
will take place resulting in no further contribution of aluminum to the sump
water.
The following conservatisms were included in the calculation of aluminum
release in support of chemical effects testing:
1. The maximum expected temperatures of the sump and spray water were
used during the corrosion calculations for each time interval.
2. The maximum expected pH values were used during the corrosion
calculations for each time interval.
3. No credit was taken for the possible inhibitory effect of silicate or other
species on aluminum corrosion.
4. No credit was taken for the presence of any oxide films formed on the
aluminum surfaces prior to the LOCA.
5. All the aluminum released by corrosion enters the solution, i.e., no
aluminum oxides remain on the aluminum surfaces.
6. No credit was taken for the effect of the presence of oxygen in the sump
water. Literature data suggest the corrosion rate of aluminum in aerated
pH 10 alkaline water is a factor of two lower than that measured in
nitrogen-deaerated water.
7. No credit was taken for the decrease in corrosion rate as a factor of
exposure time that results from the development of a passive film.
Based on these conservatisms, it is believed that the aluminum release into
the sump water is significantly overestimated.
The total aluminum mass released to the sump water was calculated using
the aluminum release rate equation above along with the North Anna-specific
aluminum inventory based on exposure category, sump and spray water pH,
and sump and spray water temperatures for specific time intervals following a
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Docket Nos. 50-338 and 50-339
Attachment 1
Page 26 of 42
LOCA. Data from the North Anna LOCA analysis was evaluated to determine
the maximum containment sump and spray water pH as input to the chemical
effects evaluation. The sump and spray water pH values for corresponding
time intervals following a LOCA are provided in Table 3.o-1.
Table 3.o-1: Summary of Post-LOCA Sump and Spray Water pH
Time Interval after
LOCA (sec.)
Maximum Sump pH
Maximum Spray pH
0 - 4 hours
8.2
10.5
4 hours - 30 days
8.1
8.1
The calculation of sump aluminum mass assumed a long-term sump and
spray pH of 8.5 for conservatism and a spray pH of 10.5 for the first 4 hours
following a LOCA, along with the containment sump and water vapor (spray)
temperatures tabulated in Table 3.0-2.
The precipitation behavior of aluminum hydroxide under representative North
Anna Units 1 and 2 post-LOCA sump water conditions was further evaluated
in bench-top testing.
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Docket Nos. 50-338 and 50-339
Attachment 1
Page 27 of 42
Table 3.o-2: Containment Sump and Water Vapor Temperature
Time Interval after
Maximum Vapor
Maximum Sump
LOCA (sec.)
Temperature (OF)
Temperature (*F)
0-20
270
240
20-150
270
270
150-600
255
265
600-1,200
250
260
1,200-1,800
240
250
1,800-2,400
240
235
2,400-3,000
235
228
3,000-3,800
225
225
3,800-4,200
205
218
4,400-7,200
185
215
7,200-14,400
135
180
14,400-28,800
135
160
28,800-57,600
135
140
57,600-86,400
135
135
86,400-172,800
135
130
172,800-259,200
135
125
259,200-30 days
110
120
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Docket Nos. 50-338 and 50-339
Attachment 1
Page 28 of 42
Bench-Top Testing
Bench-top testing was conducted to gain an understanding of the chemistry to
be expected in reduced-scale testing. The bench-top testing consisted of the
following tasks:
*
Precipitation Testing of Aluminum Hydroxide
*
Dependence of Walnut Shell Properties on Chemistry
Precipitation Testing of Aluminum Hydroxide
AECL conducted bench-top tests to determine aluminum solubility under the
worst-case conditions expected in the post-LOCA sump water. Two series of
tests were conducted: station-specific precipitation tests and aluminum
solution stability tests. In the station-specific precipitation tests, the sump
water chemistry conditions that are expected to exist after 30 days were used
for determination of aluminum precipitation. These chemistry conditions are
considered the most conservative since after 30 days, the temperature of the
sump water has decreased to a stable, low value, and the dissolved
aluminum concentration has reached its maximum value. For additional
conservatism, a pH of 7.0 was maintained since this is the lowest expected
sump pH based on accident analysis.. The concentration of aluminum used
for the bench-top testing was 44 mg/L, which was based on preliminary
determinations of the aluminum inventory in containment and the post-LOCA
containment sump water pH and temperature. The use of this high aluminum
concentration provided conservative bench-top test results. In the aluminum
solution stability tests, it was sought to determine pH values at which 2.5 to
100 mg/L aluminum solutions remained kinetically stable for 30 days.
The station-specific bench-top tests for aluminum precipitation were
conducted in three flasks identified as Warm, RT (room temperature), and BL
(blank). The flasks were maintained at 1400F and two (Warm and RT)
included insulation debris. All three of the flasks contained borated water to
which sodium aluminate was added. The solutions were stirred slowly with a
magnetic stirrer and once the pH was adjusted to the target value, the
solutions were allowed to stand for 30 days. The pH was nearly constant
throughout the 30 days. Turbidity measurements were taken for the Warm
and RT flasks daily (at test temperature for the Warm flask samples and at
room temperature for the RT flask samples). The mass of any precipitate
formed after 30 days was determined by filtering the BL solution through a
0.1-pm pore size filter, drying the filter, and then weighing the dried filter;
however, very little precipitate formed in any of the tests. Samples of the BL
filtrate were taken for elemental analysis using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES).
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 29 of 42
A measurable mass of precipitate was recovered from the North Anna benchtop test solution, indicating that precipitation is predicted at the 44 mg/L
concentration of aluminum used in the bench-top tests. Based on elemental
analysis, the precipitate was determined to consist of mainly Al and 0
indicating the formation of aluminum hydroxide or oxyhydroxide species.
The aluminum solution stability tests consisted of two parts: the first, a
titration of aluminum solutions starting at high pH against nitric acid, was used
to establish lower limits at which precipitation would occur; the second
brought aluminum solutions down to 1 pH unit above the established lower
limit and monitored the turbidity over 30 days. Tests were conducted at room
temperature, 104'F, and 140'F.
The results provided a stability map of Al concentration vs. pH in which the
North Anna station-specific conditions were predicted to be unstable with
respect to aluminum precipitation.
Dependence of Walnut Shell Properties on Chemistry
Walnut shell powder is used in the debris head loss tests to simulate epoxy
coating which is conservatively anticipated to be broken into very small
particulate sizes (nominally 10pm) post-LOCA. Tests were carried out as part
of the bench-top testing to determine if exposure to chemicals would dissolve
or alter the walnut shell particulate.
Particle size and dissolution tests carried out to characterize the effects of
exposure of walnut shells to borated water containing sodium aluminate
showed no obvious change on particle size distribution or particle
morphology. Measurements of the total organic carbon in the test solution
gave inconsistent results with respect to the amount of walnut shell
dissolution, while measurements of the weight change suggested a maximum
weight loss of 12%. No significant effect on the results of reduced-scale
testing is expected from walnut shell dissolution or weight change.
Reduced-Scale Testing
Reduced-scale testing was conducted for North Anna Units 1 and 2 to
determine the debris bed head loss. Two different test rigs were used to
perform the testing. Test Rid 33 was used to determine total strainer size
requirements, as described in Section 3.f of the previous supplemental
response (Dominion letter dated February 29, 2008), but was not used for the
reduced-scale chemical effects testing. To expedite reduced-scale chemical
effects testing, a multi-loop test rig, Test Rig 89, was designed and
constructed to facilitate the performance of concurrent testing of multiple
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 30 of 42
strainer configurations and post-accident containment sump conditions for
several of Dominion's nuclear units (i.e., Surry, North Anna and Millstone).
The differences in debris-only head loss testing results for the two different
test rigs were evaluated during the North Anna Chemical Effects Audit
performed by NRC staff in 2008 (Reference North Anna Power Station Audit
Report dated February 10, 2009, ADAMS ML090410626). The NRC staff
ultimately concluded that, although the reasons for differences in head loss
for the two test rigs could not be definitively identified, the significant
conservatisms incorporated into the sump strainer performance analysis
bound the uncertainties associated with the formation of debris beds in the
multi-loop Test Rig 89.
Test Description
Reduced-scale chemical effects testing was performed to establish the
influence of chemical products on the head loss across the containment sump
strainer surfaces after a LOCA. Tests were carried out for North Anna Units 1
and 2 RS and LHSI strainers using the multi-loop Test Rig 89. Fibrous and
particulate debris and chemicals were added into the test rig to simulate the
plant-specific chemical environment present in the water of the containment
sump. Each test was operated for more than 30 days, after the formation of a
debris bed and initial chemical addition, at a specified temperature and flow
rate to assess the possibility of precipitate formation and subsequent head
loss change. The following includes descriptions of the test facility, debris
load, chemical environment, and the chemical addition procedure.
Test Facility
The test facility consists of six single test loops. Each test loop has the same
configuration except that the strainer box orientation and fin pitch distance
may be different. Each single test loop. includes a 16 in. x 16 in. x 36 in.
strainer box (volume approximately 40 gal) and a 12 in. diameter x 18 in. long
cylindrical debris addition tank (volume approximately 9 gal). Two fins were
installed inside each strainer box with a pre-determined pitch distance. The
fins have perforated material on the sides facing each other, while the sides
facing away from the other fin have cover plates to cover the fin holes. For
North Anna testing, the fins and strainer boxes were horizontally oriented to
simulate the installed RS and LHSI strainer module orientation. The topside
and underside of the strainer box have clear windows to enable observation
of any precipitates and the debris bed on the strainer screens inside the box.
Stainless steel tubes and fittings are utilized to connect the strainer box to
other components of the loop. The loop is capable of producing flow rates
from 1 to 20 gpm. The flow rates can be adjusted via a variable frequency
drive. A magnetic flow meter is installed to provide feedback for constant flow
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Docket Nos. 50-338 and 50-339
Attachment 1
Page 31 of 42
rate control. Each loop is equipped with a 6kW in-line stainless steel heater
to provide heating to a maximum temperature of 140°F (600C). Cooling is
provided by an in-line stainless steel cooler using service water. Figure 3.o-1
provides a representation of a single loop of the Test Rig 89 multi-loop test
facility.
Physical debris including fiber and particulate, and chemicals including liquid
solutions, can be added through the debris addition tank. The debris addition
tank is equipped with a paddle-type stirrer to keep the debris suspended, and
mixed debris can be slowly metered out of the tank. Each test loop is
connected to a header tank located at an elevation of 15 feet above floor
level. The header tank can be used to accommodate extra fluid from debris
addition or thermal expansion and to control the loop pressure. Chemical
solutions can also be added in small quantities via the chemical injection
points.
Each loop is instrumented with a thermocouple to measure the water
temperature and a flow meter to measure the flow rate through the test loop.
The strainer box is instrumented with a differential pressure transmitter for
measuring the debris bed head loss. Two manual pressure gauges are also
connected upstream and downstream of the test screen to allow for
verification of the pressure and to provide back-up measurements in case the
differential pressure transmitter should fail. The pump speed, heater and
cooler are controlled by a programmable logic controller (PLC). The water
temperature and flow rate and the debris bed head loss are monitored and
recorded by the PLC. Monitoring of pH, turbidity, and concentrations of
elements in solution is via grab samples.
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Docket Nos. 50-338 and 50-339
Attachment 1
Page 32 of 42
Figure 3.o-1: Test Rig 89 Single Test Loop (One of Six)
Debris Load
Debris composition for the reduced-scaled chemical effects testing for the
North Anna Units 1 and 2 sump strainer was the same as was used for the
strainer head-loss testing as described in the previous supplemental
response (Dominion letter dated February 29, 2008) for "Break BK2" (the
limiting debris source). Test debris quantities were directly scaled from the
total debris by the ratio of the total modeled strainer area to the test section
area, termed the "debris-scaling factor." The Rig 89 RS strainer test module
area is 5.74 ft 2 while the total modeled area was 4210 ft2 . Therefore, the RS
strainer debris-scaling factor is 733.4. The LHSI strainer debris-scaling factor
is 284.0 since the LHSI strainer test module area is 5.74 ft2 and the modeled
surface area is 1630 ft2 .
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 33 of 42
The full particulate debris load for each test was added at the start of the test,
and then additions of fibrous debris were made in 1/16 in. theoretical bed
thickness increments. The theoretical bed thickness is defined as the
uncompressed fiber volume divided by the test module surface area. The first
fiber addition (1/16 in.) was made 30 minutes after the addition of the
particulate debris. The second fiber addition (an additional 1/16 in.) was
made 30 minutes after the first addition. Subsequent fiber additions were
only made once the pressure increase resulting from previous additions had
stabilized (changed by less than 5% or 0.01 psi, whichever was greater, and
exhibited no general steadily increasing trend in pressure, within 25 minutes
(approximately five tank turnovers)). Fiber additions were continued until the
debris bed thickness had reached the thin bed thickness as determined by
previous thin bed tests (1/4 inch).
Chemical Environment
North Anna-specific post-LOCA sump Water chemical conditions at the end of
the 30-day mission time for ECCS were simulated in the reduced-scale tests.
The water was maintained at the conservatively low minimum pH limit of 7.0
to enhance precipitate formation. Sodium aluminate (NaAIO 2 ) was added to
the test solution, after the particulate addition and debris bed formation, to
produce the desired concentration of aluminum in solution. The test fluid also
included boric acid and sodium hydroxide concentrations that were equivalent
to the expected post-LOCA sump water conditions.
Chemical Addition Procedure
After the debris bed was formed and the pressure drop had stabilized, sodium
aluminate solutions were added into the loop through the chemical injection
points. Over the course of the test, 19 sodium aluminate additions were
made to the LHSI strainer test loop, for a total 52.77,g NaAIO 2 , and 24
sodium aluminate additions weremade to the RS strainer test loop, for a total
69.37 g NaAIO 2 .
Precipitate Generation
Chemical additions for the chemical effects testing were accomplished by
addition of sodium aluminate solutions into the test loop through chemical
injection points in the test rig. Aluminum precipitates were generated in-situ,
mainly on the fibers and particles, by a heterogeneous precipitation mechanism.
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Docket Nos. 50-338 and 50-339
Attachment 1
Page 34 of 42
Chemical Injection into the Loop
Three methods of sodium aluminate addition were employed through the course
of the testing. Each method was successively developed in an attempt to
approximate more closely the aluminum release rate into solution in the postLOCA containment sump.
Method A. The first method used an injector to inject 3.6 L (or less) of 200 mg/L
Al solutions over 20-30 minutes, repeated every hour as necessary. The sodium
aluminate was added every 3 days to approximate the predicted aluminum
release rate into solution. Solutions of sodium aluminate were made with
borated loop water (water obtained from the test rig) adjusted to pH 12 to
facilitate dissolution of sodium aluminate. The advantages of this addition
method were that the test rig water volume was kept constant, and there were no
dilution effects on other chemicals. The disadvantage was that, since sodium
hydroxide was added to the loop water, it was necessary to add nitric acid to
adjust the loop pH back to 7.0. It was found that the follow-up nitric acid addition
caused precipitate to form in localized low pH environments around the addition
point.
Method B. The second method also used an injector, as described above. In this
method, deionized water was used to dissolve the sodium aluminate. To
compensate for the dilution of the test loop solution caused by the addition of the
deionized water, boric acid dissolved in loop water was added to the loop in a
separate step. The combined effect of (basic) sodium aluminate additions and
(acidic) boric acid additions was that the loop pH remained stable, and nitric acid
additions were no longer required. After a number of injections, the aluminum
concentration did not reflect the expected concentration, and a third injection
method was instituted.
Method C. This method used a metering pump for the sodium aluminate
additions, which permitted a more favorable mixing environment for the sodium
aluminate and avoided the addition of slugs of solution with a high aluminum
concentration. For each addition, 3.5 L of 200 mg/L Al solution was metered into
the test loop at a flow rate of 545 mL/hr. As in Method B above, deionized water
was used as a solvent for the sodium aluminate and boric acid dissolved in loop
water was injected in a separate step.
The amount of injected aluminum at the end of the test was 60.4 mg/L of which
2.6 mg/L remained in solution for the LHSI strainer test, and 79.4 mg/L of which
2.3 mg/L remained in solution for the RS strainer test.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 35 of 42
Technical Approach to Debris Transport
North Anna plant-specific analysis determined the amount and type of debris that
could be generated and transported to the sump strainer post-LOCA. Essentially
all debris (or applicable surrogate) that is analyzed to reach the containment
sump strainer was included in the reduced-scale testing. RMI debris was not
included in the chemical effects test, as RMI does not affect debris bed formation
or the resultant head loss when present in the. relatively small quantities existing
in North Anna Units 1 and 2.
Head-Loss Testing Without Near-Field Settlement
No specific credit was taken for near-field debris settlement in the strainer head
loss analysis for chemical effects.
Debris was added during the tests by mixing in the debris addition tank and then
slowly metering into the strainer test box. A mixer was used in the debris
addition tank to prevent debris settling on the floor of the tank. A magnetic brush
was used intermittently to sweep the strainer box floor in an attempt to keep
fibrous debris from settling. At the end of the tests, the amount of debris
attached to the strainer module fins was measured, with the following results:
RS Strainer Test:
LHSI Strainer Test:
97%
95%
Test Termination Criteria
The termination criteria used for the tests are described below.
1. Little or no precipitate forms in 30 days; aluminum concentrations in solution
remain at the specified value (10.3 mg/L).
2. Precipitate forms and the head loss exceeds the allowable debris bed head
loss or the available test rig NPSH margin.
3. Precipitate forms but criterion 2 is not met. Aluminum will be added to the test
loop to maintain the specified concentration until the maximum mass of
aluminum, scaled to the aluminum release mass based on containment
aluminum inventory, is added.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 36 of 42
Data Analysis
Test ProcedureSummary
Each test loop of the reduced-scale multi-loop test rig had a volume of 200 L, and
each head tank had a volume of about 30 L. Each test strainer module had a
surface area of 5.74 ft2 . To begin each test, the chemical environment was
established by filling each loop with a pH 7 boric acid solution (2800 mg/L B).
Test solution temperature was maintained at 104 0 F for the tests, and, for
comparison, allowable debris bed head losses were corrected for temperature
using the dynamic viscosity ratio. Particulate debris was added followed by
fibrous debris that established a debris thin bed. Once the head loss had
stabilized, chemical additions began.
Throughout the tests, daily water samples were taken for ICP-AES analysis to
determine the concentrations of Al, B, Ca, Fe, K, Na, P, and Si. Sample analysis
results consistently showed much lower concentration of aluminum in the test
solution than was calculated based on sodium aluminate additions, indicating
that the aluminum had either precipitated or deposited (plated out) on surfaces
such as the debris bed.
Aluminum additions were made to the test loops in an attempt to reach a test
strainer aluminum load equivalent to the containment strainer aluminum load
resulting from a 10.3 mg/L Al concentration in the containment sump. The
strainer aluminum load was determined by calculating the total expected
aluminum mass in the proportioned sump volume for the individual strainer
(either LHSI or RS strainer) and dividing by the individual strainer surface area.
The proportioned sump volume is the total sump volume proportioned by the
individual strainer flowrate relative to the total strainer flowrate.
After chemical additions were completed, the test temperature was reduced to
70°F to evaluate the effect of temperature on head loss. A flow sweep was
performed by reducing flow to 90%, then 80%, then back to 100% to evaluate the
response of head loss to flow velocity changes.
Test Results
In the North Anna LHSI test (identified as test NA-LHSI-C1), there were 19
additions of aluminum over the duration of the test (in the form of sodium
aluminate solutions), resulting in reaching a 2.31 g/ft2 strainer aluminum load.
The allowable debris bed head loss limit of 3.2 psi1 was exceeded during the
1 The
head loss limits determined previously for debris bed head loss testing (see the original
supplemental response in Dominion letter dated February 29, 2008) were established as the test criteria
for the LHSI and RS strainer chemical effects testing. Subsequently, final head loss criteria were
developed and are compared to debris bed test results in Section 3.f, Table 3.f-2 of this attachment.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 37 of 42
test. Data analysis determined that the 1 1 th Al addition, which resulted in
1.18 g/ft2 strainer aluminum load, produced an acceptable 2.9 psi head loss.
In the North Anna RS test (identified as test NA-RS-C2), there were'24 additions
of aluminum in total resulting in reaching a 3.09 g/ft 2 strainer aluminum load. The
allowable debris bed head loss limit of 2.7 psi1 was exceeded during the test.2
Data analysis determined that the 1 4 th Al addition, which resulted in 1.58 g/ft
strainer aluminum load, produced an acceptable 2.6 psi head loss.
A summary of the test head loss results are presented in Table 3.0-3.
The pressure drop curves (head loss across the strainer section vs. time) for the
LHSI and RS strainer tests are provided in Figures 3.0-2 and 3.0-3, respectively.
The curves indicate debris addition, aluminum addition, temperature changes,
and flowrate changes during the test and the corresponding effect on strainer
head loss.
Evaluation of Results
In both the North Anna LHSI and RS strainer tests, the allowable debris bed
head loss was exceeded prior to adding the maximum aluminum to the test
solution.
The maximum sump aluminum load that could be tolerated by the LHSI strainer
was determined to be 1.18 g/ft2, which is equivalent to 5020 g total sump
aluminum load. The maximum sump aluminum load that could be tolerated by
the RS strainer was determined to be 1.58 g/ft2 , which is equivalent to 8790 g
total sump aluminum load. Therefore, the sump aluminum load was determined
to be limited to 5020 g by the LHSI strainer.
Sump Chemical Load Calculation
The aluminum inventory in containment that is subject to corrosion post-LOCA
was evaluated for aluminum release to the sump water using a reduced pH of
8.5, which remains conservative with respect to the expected pH post-LOCA (see
Table 3.o-1). The calculated sump aluminum load of approximately 4943 g is
expected to be released within 30 days of event initiation based on the current
North Anna Unit 2 aluminum inventory, which is limiting for both units. The
expected aluminum release post-LOCA is less than the limiting sump aluminum
load of 5020 g. Therefore, conservatively assuming all aluminum released to the
containment sump water results in increased head loss across the strainer debris
bed, the resulting head loss would be kcceptable.
Programmatic controls have been established as part of the design control
process and containment close-out verification following maintenance or
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 38 of 42
refueling operations to limit the amount of aluminum bearing materials inside
containment during operation such that the calculated aluminum release limit will
not be exceeded.
Table 3.o-3: Summary of Test Rig 89 Chemical Effects Test Results
Rig 89 Test Loop
Test Loop
Temperature (*F)
Test Loop
Flowrate (gpm)
Strainer
Aluminum Load
(g1ft 2)
Head Loss
Test/Limit
(psi)
104
14.26
0
0.74/3.2
104
14.26
1.18
2.9/3.2
104
14.26
2.31
3.7a
104
12.43
2.31
2.9 / NA
104
11.19
2.31
2.4 /NA
104
9.94
2.31
1.9 /NA
~LH,$sl'Stainer Test
NA-LHSI-C1
(prior to Al
addition)
NA-LHSI-Cl
(Al addition at
head loss limit)
NA-LHSI-Cl
(end of Al addition)
NA-LHSI-C1
(flowrate reduction
to 12.43 gpm)
NA-LHSI-Cl
(flow sweep 90%)
NA-LHSI-Cl
(flow sweep -
3'.2
80%)
NA-LHSI-C1
(flow sweep 104
12.43
2.31
2.9/NA
100%)
NA-LHSI-C1
(temperature
70
12.43
2.31
2.4 / NA
reduction)
NA-LHSI-Cl
(flow sweep 70
11.19
2.31
1.9 / NA
90%)
NA-LHSI-Cl
(flow sweep .70
9.94
2.31
1.7 / NA
80%)
NA-LHSI-Cl
(flow sweep 70
12.43
2.31
2.4/ NA
100%)
a. Head loss peaked at 5.41 psi after the 19"' Al addition, then abruptly dropped to 2.1 psi possibly due to debris bed break caused by high differential pressure - and subsequently
recovered to 3.7 psi.
b. Head loss initially increased to 3.1 psi during temperature reduction, then decreased to 2.4 psi.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 39 of 42
Table 3.o-1: Summary of Test Rig 89 Chemical Effects Test Results (cont.)
Rig 89 Test Loop
R.
Te st
NA-RS-C2
(prior toAI
Strainer
Head Loss
Test Loop
Flowrate (gpm)
..
Aluminum Load
(gift2 )
....
Test/Limit
(psi
104
17.2
0
0.3/2.7
104
17.2
1.58,
2.6/2.7
104
17.2
3.09
3.88c / 2.7
104
10.23
3.09
1.6/ NA
.104
9.21
3.09
1.34 /NA
104
8.18
3.09
1.09 /NA
104
10.23
3.09
1.64 / NA
70
10.23
3.09
1.81 /NA
70
9.21
3.09
1.5 /NA
70
8.18
3.09
1.22 / NA
70
10.23
3.09
1.81 / NA
Test Loop
Temperature (OF)
.._ _ _ _ _ _ _ _. . .....
..
addition)
NA-RS-C2
(Al addition at
head loss limit)
NA-RS-C2
nd of Al
(end of Al addition)
NA-RS-C2
(flowrate reduction
to 10.23 gpm)
NA-RS-C2
(flow sweep 90%)
NA-RS-C2
(flow sweep 80%)
NA-RS-C2
(flow sweep 100%)
NA-RS-C2
(temperature
reduction)
NA-RS-C2
(flow sweep
90%)
NA-RS-C2
(flow sweep -
-'
80%)
NA-RS-C2
(flow sweep -
100%)
c. Head loss peaked at 4.38 psi after the 20(n Al addition, then abruptly dropped to 2.7 psi possibly due to debris bed break caused by high differential pressure.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 40 of 42
Figure 3.0-2: Test NA-LHSI-CI Chemical Effects Test - Head Loss vs. Time
NA-LHSI Chemical Effects Test
45
6
40.5
5.4
36
4.8
c•
31.5
4.2
3.6
CL
S27
0
0)
0
22.5
~-18
2.4
13.5
1.8
E 9
1.2
I-
J-4.5
0.6
0
0
02/05/08
17/05/08
01/06/08
16/06/08
01/07/08
16/07/08
31/07/08
0:00
0:00
0:00
0:00
0:00
0:00
0:00
Time (standard)
15/08/08
0:00
-J
M
'
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 41 of 42
Figure 3.0-3: Test NA-RS-C2 Chemical Effects Test - Head Loss vs. Time
NA-RS-C2 Chemical Effects Test
45 -
5
----------------- --------------------------- --------Temperature (0C)
24th
Foat(UGM---------------17th ---------
40.5
36
----
31.5
Head loss(PSI)
-
0
-
--
16th-------
3.5
2--h
3
2.5
I15th
Z-
........
18
--
|3
1
-
-At
-5-
3rd A
E--------------------6th
! 5t
4)
A[ ---
4
--------------
27
UE 22.5
-- 4.5
Al
Al--------------Al
3rdlfibe
18th
21th----
19th
0.
00t
13/05/08 24/05/08 05/06/08 16/06/08 28/06/08 09/07/08 21/07/08 01/08/08 13/08/08
0:00
12:00
0:00
12:00
0:00
12:00
0:00
12:00
0:00
Time (standard)
(Aa
0
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 1
Page 42 of 42
3.p
Licensing Basis
Dominion's February 29, 2008 supplemental response discussed the licensing
bases changes that had been implemented for North Anna Units 1 and 2
associated with the resolution of the sump issues considered in GSI-191 and GL
2004-02 in the form of Updated Final Safety Analysis Report (UFSAR) Revisions,
analysis methodology changes, and license amendment requests.
A UFSAR change and Technical Specifications Bases change were made to
establish the limit for the long-term containment sump pH to 8.5 from 9.5 to be
consistent with the calculation of sump aluminum load discussed in Section 3.o.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
ATTACHMENT 2
RESPONSE TO GENERIC LETTER 2004-02 AUDIT OPEN ITEMS
NORTH ANNA POWER STATION UNITS 1 AND 2
VIRGINIA ELECTRIC AND POWER COMPANY
(DOMINION)
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 2
Page 1 of 6
Responses are provided to GL 2004-02 Audit Open Items not resolved in the previous North Anna supplemental response
(Dominion letter dated February 29, 2008).
NRC GL 2004-02 AUDIT OPEN ITEMS
NORTH ANNA UNITS I AND 2
Open Item No.
and Subject
Open Item 5.3-1
Downstream Effects-Core
Blockage
Item
Although downstream evaluations were in
progress during the audit, the licensee has not
made any final conclusions as to whether the
cores at North Anna Power Station could be
Resolution
See Section 3.n "Downstream Effects - Fuel
and Vessel" for Dominion's response to this
open item.
blocked by debris following a LOCA, and this
area is incomplete. The licensee should
summarize the method and results of its
evaluation of this issue in its GL 2004-02.
supplemental response.
Open Item 5.3-2
Downstream Effects
Evaluations Preliminary
See Section 3.m "Downstream Effects The licensee's evaluations of the downstream
effects of debris on systems and components are Components and Systems" for Dominion's
response to this open item.
preliminary, based in part on the generic
methodology of WCAP-16406-P which is under
review by the NRC staff. NAPS will reassess the
evaluation based on the conclusions and findings
associated with the staff's review of WCAP16406-P Revision 1. The licensee should
provide the staff a summary of the method and
results of this evaluation.
Serial No. 09-003
Docket.Nos. 50-338 and 50-339
Attachment 2
Page 2 of 6
NRC GL 2004-02 AUDIT OPEN ITEMS
NORTH, ANNA UNITS 1 AND 2
Open Item No.
Item
Resolution
and Subject
Open Item 5.3-3
I tLocations
The evaluation documented that the ECCS
instrument locations are adequate because of an
assumption of "good engineering practice." This
See Section 3.m "Downstream Effects Components and Systems" for Dominion's
response to this open item.
assumption needs to be verified, such as by
means of isometrical drawings or an ECCS
survey. The licensee should provide the staff a
summary of the method and results of this
verification.
Open Item 5.3-4
Debris Bypass Testing
The licensee had not made a final determination
on how the bypass testing data is going to be
implemented in the downstream effects
evaluation for ECCS and internal vessel
components. The licensee should provide the
of the testing."onsremEfecs
method and results of its
staff a summary
bypas
bypass testing. :Components
See Section 3.n in previous North Anna
supplemental response (Dominion letter dated
February 29, 2008) for a detailed discussion on
bypass flow testing with respect to the vessel
and core.
See Section 3.m "Downstream Effects and Systems" for Dominion's
response to this open item with respect to
components and systems.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 2
Page 3 of 6
NRC GL 2004-02 AUDIT OPEN ITEMS
NORTH ANNA UNITS 1 AND 2
Open Item No.
and Subject
Open Item 5.3-5
Fixed Throttle Valve Setting
Item
The downstream component evaluation did not
reference operating procedures or testing history
in order to demonstrate high confidence that
throttle valves will remain in their fixed position
during ECCS operation. Throttle valve fixed
position is the basis for assuming the system's
hydraulic resistance to be fixed. The licensee
should address the-full potential range of throttle
valve positions in their revised downstream
evaluation.
The licensee did not quantify seal leakage
andassociated with downstream effects into the
Quantification adAuxiliary
Building, nor evaluate the effects on
Assessment of Downstream
equipment qualification, sumps and drains
EfectkTatg
aseSa
operation, or on room habitability. The licensee
summarize the method and results of its
Leakageshould
evaluation of these subjects in its GL 2004-02
supplemental response.
Open Item 5.3-6
Resolution
See Section 3.mn "Downstream Effects Components and Systems" for Dominion's
response to this open item.
Throttle valves are locked in their fixed position
and are not affected by debris in the
recirculation fluid.
See Section 3.mn "Downstream Effects Components and Systems" for Dominion's
response to this open item.
Mcaia elpromnei o desl
affected by debris in the recirculation fluid.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 2
Page 4 of 6
NRC GL 2004-02 AUDIT OPEN ITEMS
NORTH ANNA UNITS I AND 2
Open Item No.
and Subject
Item
Resolution
Open Item 5.3-7
Range of System Flows
The licensee did not fully-define the range of fluid
velocities within piping systems. Fluid velocities
used were based on nominal system operating
characteristics and did not take into account the
range of possible system flows. NAPS staff
should re-assess ECCS flow balances based on
the results of system and component wear
evaluations and should provide a summary of the
method and results to the NRC staff.
See Section 3.m "Downstream Effects Components and Systems" for Dominion's
response to this open item.
Component wear is not significant and has a
negligible effect on system flow.
Open Item 5.3-8
The preliminary downstream component
evaluation did not consider the use of minimum
and maximum system operating points; instead,
best-efficiency performance values were used.
See Section 3.m "Downstream Effects Components and Systems" for Dominion's
response to this open item.
Component wear is not significant and has a
ECCS Minimum and
Maximum Operating Points
The ECCS operating point values were not
referenced back to system bases calculations.
The licensee should evaluate this issue and
provide a summary to the staff.
negligible effect on system flow.
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 2
Page 5 of 6
NRC GL 2004-02 AUDIT OPEN ITEMS
NORTH ANNA UNITS 1 AND 2
Open Item No.
and Subject
Open Item 5.3-9
Use of Manufacturer's Pump
Performance Curves
Item
The pump performance inputs considered in the
preliminary downstream components evaluation
were obtained from manufacturer's pump
performance curves. The evaluation should
consider the use of degraded pump curves or in-
See Section 3.m "Downstream Effects Components and Systems" for Dominion's
response to this open item.
represent actual system operating conditions.
The licensee should evaluate this issue and
provide a summary to the staff.
pump performance curves.
The licensee had yet to perform an overall
system evaluation that integrates the results of
the downstream components evaluation. The
evaluation should address compliance with 10
CFR 50.46, "Long Term Core Cooling." The
licensee should evaluate this issue and provide a
summary to the staff.
See Section 3.m "Downstream Effects Components and Systems" for Dominion's
response to this open item.
beter
crve better
asthee
estng
urvs
servce
service testing
curves
as
these curves
Open Item 5.3-10
Overall Downstream ECCS
Evaluation
Resolution
terconse wit
manuater's
determi
with manufacturer's
determined
pm
efracto be consistent
uvs
Serial No. 09-003
Docket Nos. 50-338 and 50-339
Attachment 2
Page 6 of 6
NRC GL 2004-02 AUDIT OPEN ITEMS
NORTH ANNA UNITS 1 AND 2
Open Item No.
and Subject
Open Item 5.4-1
Evaluate Chemical Effects
Item
The licensee's chemical effects analysis was
incomplete at the time of the audit. Also, the
licensee has not evaluated the contribution of
coatings to chemical effects by: (1) leaching
constituents that could form precipitates or affect
other debris; and (2) changing form due to the
pool environment. Since the licensee's
integrated chemical effects testing plans have
not been completed, the staff could not review
the application of the debris bed head loss
acceptance criteria to verify that the long-term
and short-term acceptance criteria are bounding
with respect to intermediate conditions. The
licensee should provide the staff a summary of
the method and results of its chemical effects
evaluation and testing.
Resolution
See Section 3.o "Chemical Effects" for
Dominion's response to this open item.